The invention relates to a circuit grinding apparatus with a high-pressure roller mill for pressure disintegrating granular material and with at least one integrated sifter where both units are disposed within two stationary side walls between which a material conveyor ring is rotatably seated on rolls and capable of being set into rotation for an internal circulation of material and where the inflow of material takes place through one or more openings in one or in both housing side walls from the side and the material likewise exits laterally through one or more openings in the housing side wall.
A milling device of the above type (DE-A 197 26 523, U.S. Pat. No. 6,032,887), whose disclosure is incorporated herein by reference is a highly compact circuit grinding apparatus with a high-pressure roller mill or roller press for pressure disintegrating or material bed disintegrating granular material and with an integrated sifter. The roller mill or roller press with its two rollers is encompassed by a housing comprising two stationary, i.e., non-rotating side walls between which a rotatably seated material conveyor ring, which can be set into rotation by means of a rotary actuator, is disposed for an internal circulation of material. In the known grinding apparatus, in the working area within the rotating material conveyor ring below the nip of the roller press, a static and/or dynamic sifter is integrated through which the sifter air flows, and the coarse grain portion or oversized material discharged by the sifter or sifters falls downward onto the cylindrical inside surface of the rotating material conveyor ring. This conveyor ring carries the press discharge material (scab material) or oversized material de-agglomerated in the sifting upward into the area of the upper vertex point of the ring from where said material falls from the top into the feeder shaft of the roller press, thus creating the internal circulation of material. At the same time, the sifter air flow loaded with the fine grain portion of the grinding material is drawn out of the working area and is separated from the fine grain portion outside of the circuit grinding apparatus. In such a compact circuit grinding apparatus the sifter integrated in the rotating material conveyor ring can be disposed above instead of below the roller press (DE-A-196 30 687, U.S. Pat. No. 5,918,823), the disclosure of which is incorporated herein by reference.
Therefore, in the circuit grinding apparatus of this type, bucket conveyors or other space-consuming conveyors for transporting the mill or press discharge material and the oversized sifter material to the mill or press inlet are omitted. With the rotating material conveyor ring, a multiple internal circuit of material with multiple material bed stressing of the material is thus achieved in the smallest space and with a low outlay of machinery where even high material circuit loads caused by reduced roller press pressures, for example, have to be managed.
In the known circuit grinding apparatus the material conveyor ring encompassing the roller mill and the sifter, which ring can have a large diameter of more than 10 m in industrial applications, is rotatably seated on two rolls disposed spaced apart from each other and supporting the weight of the material conveyor ring on the bottom, one of which rolls is actuated. In order to reduce the risk of deformation of the material conveyor ring having a large diameter, said ring has to be constructed relatively rigidly which results in a heavy weight. Seating the rotating material conveyor ring on more than two roll bearing stations, however, is not easily feasible because the additional bearing stations would create a statically undefined system in which the bearing rolls are not all evenly loaded.
The aim of the invention is to further develop a circuit grinding apparatus of the above described type such that the material conveyor ring, which is rotatably seated, has a very large diameter and rotates in operation, is as light in weight as possible and the rotary actuator is constructed as simply as possible.
The circuit grinding apparatus of the invention is characterized in that distributed over the bottom circumferential area of the material conveyor ring (as seen in circumferential direction) more than two, for example three or four or even more rolls are disposed supporting the material conveyor ring on the bottom, where two adjacent bearing rolls in circumferential direction of the ring are positioned at the ends of a common rocker lever, which, in turn, is supported on the machine frame via a tilting joint. Especially advantageously, one rocker lever is provided on either side of the vertical plane applied through the axis of rotation of the material conveyor ring on whose ends the bearing rolls are positioned parallel to the axis, i.e., a total of four bearing rolls or four wheel sets are provided that securely support the rotating material conveyor ring on the bottom. Because of the higher number of bearing rolls or wheel sets, the overall range of support for the material conveyor ring can be increased and the load per roll or wheel set and the pressing between the surfaces of the material conveyor ring and the rolls and the risk of deformation are reduced. The material conveyor ring can be constructed so as to be light in weight. The support rolls or bearing rolls and the actuated roll can have a small diameter, which simplifies the motor actuation of the driving roll, allowing a direct actuation of the driving wheel sets and resulting in the omission of high-maintenance elements, such as toothed gearing, propeller shafts and/or V-belt drives. If a gearing is used for the rotary actuator, its transmission ratio can be lower.
The articulated rocker lever design achieves a statically defined system for the seating of the material conveyor ring where all rolls or wheel sets are evenly loaded. This even load is maintained even when the position or the slope of the axis of rotation of the material conveyor ring changes, at least when the tilting joint of the rocker levers is a universal ball joint or a socket joint. One of the tilting joints may be a cylindrical joint with a fixed axis of rotation parallel to the axis of rotation of the conveyor ring so as to better fasten the material conveyor ring. Seating the material conveyor ring in accordance with the invention improves its concentricity. Also, the flexibility of the rocker levers and thus the bearing rolls or wheel sets reduces the negative effects caused by any circularity errors in the material conveyor ring and by any gaps between the joints of the segments of which the rotating material conveyor ring is composed.
The invention and its other characteristic features and advantages will be demonstrated in more detail by means of the schematic exemplary embodiment shown in the drawing.